1. Field of the Invention
The present invention relates to an on-vehicle communication device performing a code matching operation through a communication with a mobile device and controlling an on-vehicle equipment based on its matching result.
2. Description of the Background Art
An on-vehicle communication device mounted on a vehicle communicates with a mobile device through a modulated signal modulated by spread spectrum. Such on-vehicle communication device conventionally includes a smart entry function in addition to a remote operation function. According to the remote operation function, when an operation part of the mobile device is operated by a user, for example, a modulated transmission command signal is transmitted from the mobile device, and the on-vehicle device controls an on-vehicle equipment to lock/unlock a vehicle door, for example in response to the transmission command signal. According to the smart entry function, the mobile device automatically returns a response signal including a return code signal in response to a question signal transmitted from the on-vehicle device. Thus, the on-vehicle device performs a matching operation with the return code signal from the mobile device and locks/unlocks the door based on its matching result. According to the smart entry function performing the above operation, the door can be locked/unlocked without operating the operation part of the mobile device.
Remote control system of an on-vehicle equipment disclosed in Japanese Patent Application Laid-Open No. 5-106376 includes a mobile radio device and a vehicle radio device. According to this system, the mobile radio device has first receiving means and first transmitting means for transmitting a response signal when the first receiving means receives a call signal. Meanwhile, the vehicle radio device has second transmitting means for transmitting the call signal at predetermined time intervals, and second receiving means for receiving the response signal from the mobile radio device. Thus, the vehicle radio device has controlling means for outputting a signal for unlocking a vehicle door when the second receiving means receives the response signal and outputting a signal for locking the vehicle door after a lapse of predetermined time when the second receiving means does not receive the response signal.
Japanese Published Patent Publication No. 2003-500957 discloses a multiple-access spread spectrum communication system that evens out response times of a plurality of mobile devices for a question request signal from a vehicle, regardless of the number of mobile devices.
In addition, according to a vehicle communication device disclosed in Japanese Patent Application laid-Open No. 2003-188767, in order to speed up system synchronization of spread spectrum, a synchronous processing is performed using a plurality of partial correlating units to calculate a correlation value. Thus, when the calculated correlation value is smaller than a predetermined threshold value in a comparison operating unit for comparing the result of each partial correlating device, clock supply is stopped to prevent power consumption from being increased.
According to a conventional on-vehicle communication device, a transmission command signal is received from a mobile device and it is confirmed whether the transmission command signal is received or not periodically at the time of remote operation function. In order to confirm that, it is necessary to synchronize the transmission command signal with a PN signal, and when it takes time for the synchronization, the problem is that power consumption is increased. In order to solve this, as described above, the invention is proposed such that the synchronization time is shortened by speeding up the synchronization with the plurality of partial correlating units, and the partial correlating unit determined to be unnecessary is stopped to lower the power consumption. However, since the plurality of partial correlating units is used, the size of a circuit performing a clock operation is increased, and as a result the problem is that the power consumption is also increased.